1. Field of the Invention
The present invention relates to an apparatus for purifying liquids such as lubricating oil, machine oil, or a liquid such as water, and particularly relates to a purifying apparatus having a filter made of paper, a sheet, or fabric which is wound in the form of a roll.
2. Description of the Prior Art
U.S. Pat. No. 4,688,503 entitled "LIQUID FILTER ASSEMBLY", granted May 13, 1988 to the inventor of this application, discloses a structure, in a purifying apparatus having a roll filter member, which is effective in preventing cracks from occurring in the roll filter member. According to the proposal described in this patent, the roll filter member is firmly coaxially inserted in a metal casing having a cylindrical cross section, and a non-woven fabric sheet-like filter element is disposed on the roll filter member at its upper end surface. A perforated retainer disc having bias means is mounted on the sheet-like filter element. A contaminated liquid including impurities is pressured by a pump, led into the metal casing, and then fed to the sheet-like filter element through the holes in the disc. After being preliminarily filtered by the sheet-like filter element, the liquid is passed through the roll filter member so as to be substantially completely purified by the roll filter member. If clogging occurs as accumulated used time or accumulated filtered quantity increases, the pressure for supplying the contaminated liquid must be raised. The sheet-like filter element acts not only to operate as a primary filter but to dispersively supply pressured contaminated liquid to the roll filter member to thereby prevent cracks from occurring by concentration of the highly pressured contamination liquid at a weak portion of the roll filter member. The proposal is particularly effective in that high supply pressure necessary to obtain high efficiency can be maintained.